尾递归

https://baike.baidu.com/item/%E5%B0%BE%E9%80%92%E5%BD%92/554682?fr=aladdin
https://www.cnblogs.com/Anker/archive/2013/03/04/2943498.html
http://blog.csdn.net/fall221/article/details/9156753
http://python.jobbole.com/86937/
https://www.cnblogs.com/hello--the-world/archive/2012/07/19/2599003.html
http://blog.csdn.net/Together_CZ/article/details/76216239
http://blog.csdn.net/sinat_27522913/article/details/50732975

尾递归

原文：http://www.cnblogs.com/coder211/p/7943886.html